Boussingaultite is a double-sulfate mineral represented by the chemical formula (NH4)2Mg(SO4)2.6(H2O), which has monoclinic symmetry, forming clear crystals. The mineral Boussingaultite is water soluble, has density of 1.7 g/cm3 and is usually found in nature in regions rich in anthracite.
Boussingaultite production methods are known in the art. One example is the production from magnesite (MgCO3) according to WO 2008/013510. The use of magnesite has the disadvantage of being a very poorly soluble source of magnesium, in the form of carbonate.
Another example is the production method from kieserite (MgSO4.H2O) as a source of magnesium, according to the German patent DE 3320181. Kieserite is a more soluble source of magnesium, however, it is more costly to process, and it results in very hygroscopic salts, a disadvantage in the production of fertilizers.
This invention proposes a new process for the production of Boussingaultite, which does not present the disadvantages of the prior art processes, based on the reuse of wastewater originating from hydrometallurgical processes.
The hydrometallurgical processes for the production of metals, such as nickel, copper and rare earths, have the major drawback of generating liquid effluent rich in magnesium sulfate. This fact requires the execution of one or more stages of wastewater treatment with lime, yielding a solid residue rich in calcium sulfate (CaSO4) and magnesium hydroxide (Mg(OH)2), which must be disposed of in an appropriate location.
This invention refers to a new process for the recovery of the magnesium contained in these liquid effluents, by its precipitation in the form of a double magnesium sulfate and hydrous ammonia salt, with the molecular formula, (NH4)2SO4.MgSO4.6H2O, being called Boussingaultite.
This invention uses as a source of magnesium, for the possible production of fertilizers, wastewater originated from hydrometallurgical processes which was previously only intended for disposal. Thus, the proposed process presents economic and environmental gains over other procedures known to the state of the art.